Continuous hot dip galvanizing of metal strip



Feb. 24, 1959 w. L. DIEHL ET AL 2,875,096

' CONTINUOUS HOT DIP GALVANIZING OF METAL STRIP Filed Aug. 19, 1955 INVENTORS William L. Diehl 8| United States Patent CONTINUOUS HOT DIP GALVANIZING OF METAL STRIP William L. Diehl, St. Clairs'ville, Ohio, and'Henry S. Bell, 'Wheeling, W. Va., assignors to Wheeling SteelCorporation, Wheeling, W. Va., a corporation of Delaware Application August 19, 1955, Serial No. 529,562 '2 Claims. (Cl. 117-131) This invention relates to the .continuous hot dip galvanizing of .metal strip and .more .particularly to improved process steps and combinations of elements of apparatus which contribute importantly to the ability to produce galvanized strip of optimum quality at unprecedented speed.

As continuous line speeds have increased during the past decade or so great difiiculty has been experienced in producing by continuous hot dip galvanizing galvanized strip of uniform optimum quality. The increased speed ofpthe strip produces a strongtendencyof the strip to carry with it anexcessiveiquantity of spelter :as the'strip emerges from the bath of molten spelter and there is also a tendency for the coatingon the galvanized strip to be relativelyithickmear"the edgesfoftthei strip and relatively thin near the center of the strip.

.It is 1 possible bythe use of grooved exit or coating rolls to'counteract to some extent the above mentioned tendencies, but 'forthe'higher speeds'which are now commercial grooved exitrolls'do not adequately. serve the purpose. Moreover, while for some intermediate speeds grooved exit rolls might "be designed which would produce galvanized strip of optimum quality-for aparticular strip speed in the application of a particularweight of coating to a strip of a particular gauge, such rolls would not be satisfactory if the conditions should be substantially changed. p

'A factor which causes 'difliculty is the capillary attraction of the strip forthe spelter. The exit rolls will break down the capillary attractiontora certain :extent but their ability to do so is lessened as the strip speed and coating thickness increase. We have found it highly desirable to provide means --.engaging :the 'strip in f'the molten spelter bath before the strip reachesrth'eexit rolls to inhibit the tendency of spelter to cling to the strip, or, in other words, to break down the capillary attraction of the strip for the spelter. We desirably bring rolls to bear against the respective faces of the strip in the bath before the strip reaches the exit rolls.

The means engaging the strip in the bath before the strip reaches the exit rolls to inhibit the tendency of spelter to cling to the strip should be so positioned relatively to the exit rolls that substantial capillary attraction of the spelter to the strip cannot be set up between said means and the exit rolls. If such means are spaced too far away from the exit rolls capillary attraction between the strip and the spelter may be set up all over again before the strip reaches the exit rolls even though it has been reduced by such means. We prefer to employ opposed rolls in the bath arranged to bear against the respective faces of the strip before the strip reaches the exit rolls and thereby inhibiting the tendency of spelter to cling by capillary attraction to the strip, such opposed rolls being so positioned relatively to the exit rolls that substantial capillary attraction of the spelter to the strip cannot be set up between such rolls and the exit rolls. The capillarity reducing rolls desirably have faces resistant to wetting by molten spelter. -Such rolls may be 2,875,096 Patented Feb. 24, "1795-9 madetofgstainless steel or they maybe schromiumrplated or surfaced *with some-hard, glassy material'resistant to wettingby moltenispelter. .Materials which are resistant towetting by'molten spelter are known to those skilled in the art.

The capillarity reducing rolls are preferablyrelatively resiliently urge'd toward the strip. One of :those :rolls may bemounted for rotation about a fixed axis and the other-may .be resiliently; pressed toward the roll which is mounted fforrotation :about a fixed axis.

.The distancebetweena the capillarity reducing rolls and the exit or coating. rollsvdepends upon the speed of the strip,thes .gauge of :thesstrip and the thickness of "the galvanizedcoat-ing being :applied to the strip. v,It isrnot possible to state fempirically what that distance should bejjust 381i is not possible to state empiricallyjust what the direction and speefd of the exit rolls should be since the 'variables-whichyhave been mentioned have to be taken into consideration. However, a person skilled in the art following cur -teaching will .have {no -difficulty ascertaining the optimum direction and speed of :the exit rolls and the optimum distance between the capillarity reducing: rolls andthe exit rolls 'for a particular strip speed coupledwith a particularstrip gauge and a particular; thickness =10f coating.

Either'sgrooved .o'r:-ungrooved exit rolls may be used.

The capillarityreducing rolls may be pressed together by any convenient .rneans,the purpose being to press those -rolls againstthestrip with sufiicientpressure that as the stripadvancesitwwillcause the capillarityreducing rollsto turnby engagement with the strip. Thusn'ormally the capillarity .reducing rolls, being driven: by .the strip, turn at agperi-pheralsspeed substantially equalgto the lineanspeedof thest'rip.

:The capillarity:reducing'rolls are preferably: of smaller diameter-.thanthe exit rolls; -We have .-found that generally speaking it isndesirable to have the capillarityreduc-ing rolls .--not;.greater than about three inches, in' .diameter, They. are preferably ungrooved and as above-stated preferably have faces resistant to wetting byimolten:spelter. .Forexarnple, the capillarity reducingqrolls mayibe made of, or at least faced with,.alloy steel. I

.For very high speeds its-may be desirable to provide capillarity ,reducingrolls in tandem, i.- e., :to providez'rnore than one set of such rolls engaging the striptsuccessively as the strip advances through the spelter bathtowardithe exit rolls. 7 e I Otherdetails, objects and advantages of:.the..-invention will become apparent as the following description of a present preferred method of practicing the same proceeds.

In the accompanying drawing we have illustrated a present preferred method of practicing the invention, the figure being a fragmentary view partly in elevation and partly in vertical cross-section of a hot dip galvanizing pot incorporating our invention.

Continuous galvanizing lines are now operated at speeds above 300 feet per minute and speeds in the range 500-600 feet per minute are probable in the near future. For strip speeds in excess of speeds substantially in the range -160 feet per minute we provide for breaking the capillarity of the molten metal before the strip reaches the exit rolls to reduce the amount of molten spelter carried up by the strip.

Referring now more particularly to the drawing, there is shown a galvanizing pot designated generally by reference numeral 2 and which may be of conventional construction. It is adapted to contain molten spelter, the level of the molten spelter in the galvanizing pot 2 being indicated by the line 3. By spelter we mean any molten bath suitable for galvanizing and which is primarily zinc. The spelter may be substantially all zinc or it may have other metals admixed with the zinc, such,

for example, as aluminum, lead, antimony, cadmium, tin, etc., either singly or in various combinations.

The exit rolls, sometimes called coating rolls, are shown at 4, being mounted in conventional manner partly immersed in the molten spelter and partly extending above the surface of the molten spelter. As shown in the drawing the surface of the molten spelter is substantially at the elevation of the axes of the exit rolls 4. The exit rolls are provided with driving means which may be conventional.

The strip enters the galvanizing pot in conventional manner and passes through the molten spelter and about a guide roll 5 rotatably mounted below the surface of the spelter, the strip, which is designated by reference numeral 6, passing vertically upwardly from the guide roll 5 between the exit rolls 4 as shown.

We provide opposed capillarity reducing rolls 7 and 8 adapted to engage the strip at opposite faces thereof as shown in the drawing. The capillarity reducing rolls 7 and 8 have faces resistant to wetting by molten spelter and are relatively resiliently urged toward the strip. In the form shown the roll 7 is mounted for rotation about a fixed axis and the roll 8 is resiliently pressed toward the roll 7. The roll 8 is rotatably mounted in a pivoted mounting structure 9 which is pivoted at 10 to a stationarily mounted bracket 11. Connected with the mounting structure 9 is an outwardly extending arm 12 carrying a weight 13 which is adjustably positionable along the arm. The structure 9, the arm 12 and the weight 13 are to all intents and purposes unitary and the weight may be adjusted along the arm as desired to resiliently press the roll 8 toward the roll 7 with the desired force. The rolls 7 and 8 are both freely rotatable and are turned by the movement of the strip in contact therewith.

The rolls 7 and 8 are so positioned relatively to the exit rolls 4 that substantial capillary attraction of the spelter to the strip cannot be set up between the rolls 7 and 8 and the rolls 4. The rolls 7 and 8 reduce or break the capillary attraction of the spelter for the strip and thus cooperate with the exit rolls 4 in controlling the application of the spelter to the strip.

Subject matter originally'disclosed herein is covered in our divisional application Serial No. 724,144, filed March 26, 1958.

While we have illustrated a present preferred method of practicing the invention it is to be distinctly under stood that the invention is not limited thereto but may be otherwise variously practiced within the scope of the following claims.

7 We claim:

1. In the hot dip galvanizing of continuous metal strip in which the strip is delivered upwardly out of .4 the galvanizing bath of molten spelter between exit rolls partly immersed in the bath engaging the respective faces of the strip and arranged with their axes parallel and generally horizontal and in which the strip moves at a speed at which the spelter tends to be carried along with the strip by capillary attraction, the step of inhibiting the carrying up out of the bath of an excessive amount of molten spelter which comprises engaging the upwardly moving strip in the bath before the strip reaches the exit rolls, at a location close enough to the exit rolls that substantial capillary attraction of the spelter to the strip cannot be set up between that location and the exit rolls, by capillary attraction reducing rolls only and thereby inhibiting the clinging of spelter to the strip. 2. In the hot dip galvanizing of continuous metal strip in which the strip is delivered upwardly out of the galvanizing bath of molten spelter between exit rolls partly immersed in the bath engaging the respective faces of the strip and arranged with their axes parallel and generally horizontal and in which the strip moves at a speed at which the spelter tends to be carried along with the strip by capillary attraction, the step of inhibiting the carrying up out of the bath of an excessive amount of molten spelter which comprises engaging the upwardly moving strip in the bath before the strip reaches the exit rolls, at a location close enough to the exit rolls that substantial capillary attraction of the spelter to the strip cannot be set up between that location and the exit rolls, by capillary attraction reducing means only and thereby inhibiting the clinging of spelter to the strip.

References Cited in the file of this patent UNITED STATES PATENTS 872,368 Porter et al. Dec. 3, 1907 1,143,922 Skemp et a1. June 22, 1915 1,348,478 Corrigan Aug. 3, 1920 1,641,978 Lundquist Sept. 13, 1927 1,726,336 Brown Aug. 27, 1929 1,772,195 Steele Aug. 5, 1930 1,980,961 Sommer Nov. 13, 1934 2,236,213 Jenkins et a1. Mar. 25, 1941 2,315,150 Bobrov Mar. 30, 1943 2,364,904 Keller Dec. 12, 1944 2,577,904 McNabb et a1 Dec. 11, 1951 2,740,729 Hodil Apr. 3, 1956 FOREIGN PATENTS 496,402 Great Britain Nov. 30, 1938 OTHER REFERENCES Bablik: Galvanizing (Hot Dip) pages 432, 433, 3rd ed., 1950, Spon Ltd., London. 

1. IN THE HOT DIP GALVANIZING OF CONTINOUS METAL STRIP IN WHICH THE STRIP IS DELIVERED UPWARDLY OUT OF THE GALVANIZING BATH OF MOLTEN SPELTER BETWEEN EXIT ROLLS PARTLY IMMERSED IN THE BATH ENGAGING THE RESPECTIVE FACES OF THE STRIP AND ARRANGE WITH THEIR AXES PARALLEL AND GENERALLY HORIZONTAL AND IN WHICH THE STRIP MOVES AT A SPEED AT WHICH THE SPELTER TENDS TO BE CARRIED ALONG WITH THE STRIP BY CAPILLARY ATTRACTION, THE STEP OF INHIBITING THE CARRYING UP OF THE BATH OF AN EXCESSIVE AMOUNT OF MOLTEN SPELTER WHICH COMPRISES ENGAGING THE UPWARDLY MOVING STRIP IN THE BATH BEFORE THE STRIP REACHES THE EXIT ROLLS, AT A LOCATION CLOSE ENOUGH TO THE EXIT ROLLS THAT SUBSTANTIALLY CAPILLARY ATTRACTION OF THE SPELTER TO THE STRIP CANNOT BE SET UP BETWEEN THAT LOCATION AND THE EXIT ROLLS, BY CAPILLARY ATTRACTION REDUCING ROLLS ONLY AND THEREBY INHIBITING THE CLINGING OF SPELTER TO THE STRIP. 